Heating control apparatus



June 3, 1952 P. G. FRERER 2,599,101

HEATING CONTROL APPARATUS Filed Dec. 19, 1947 &

gwue/wto'o PAUL G. FRERER Patented June 3, 1952 2,599,101 HEATINGCONTROL APPARATUS Paul G. Frerer, Baltimore, Md., assignor to Ben dixAviation Corporation, Baltimore, Md., a

corporation of Delaware Application December 19, 1947, Serial No.792,762 3 Claims. (01. 236-9) -This, invention relates toapparatusforcontrolling automatically fired heating installations and,more particularly, to such installations in which provisions have beenincluded for forced circulation of the heat exchanging medium.

At the present time, automatically controlled oil-fired heatinginstallations are widely .em

ployed both in the domestic and commercial fields. It was early foundthat when such a system was employed in forced-air heating installationsthe energization of the circulating fan simultaneously with theenergization of the burner motor resulted in the establishment of coldair flow from the warm air register. To avoid objections raised to thischaracteristic-of operation by the public, a temperature responsiveswitch was located within the furnace plenum which governed theoperation of the circulating fan permitting such operation only when thephenum temperature exceeded a preset value. Most of these automaticallyfired heating installations were already provided with a combustionresponsive circuit controller intended to disable a slow acting safetyswitch governing burner operation after combustion had been successfullyand safely established. However, the operation of this switch continuedto be applied solely to the monitoring of burner starting conditionswhile a second device was used for governing fan operation. A It is anobject of the present invention to provide av burnercontrolled system inwhich the combustion safety monitoring mechanism also governs theoperation of an associated circulatoror circulation controlling device.

. Still another object of the inventionis to providea'n improved heatingsystem having an associated circulation controlling device with animproved arrangement for delaying the establishment of circulation afterthe initiation of combustion and for delaying the interruption ofcirculation after the cessation of combustion.

Other objects and advantages of the invention will in part be describedand in part be obvious when the following specification is read inconjunction with:

, Thesingle figure drawing which is a schematic illustration of a systemincorporating the invention.

7 Referring now to the drawing, there is shown a hot air furnace [4having a combustion chamber 16 surrounded by a heat exchanging duct 2 I.A burner I8 of the conventional gun type is situated with the deliveryend of the blast tube lo cated within the combustion chamber It. It

to be understood that the burner [8 has associated therewith a fuelsupply tank and connecting lines forming no part of the inventionwhichhave been omitted from the showing in the interest of simplicity. Theburner I8 is provided with power input terminals 84 and formergizationof the burner motonand the combustible mixture at the delivery end ofthe blast tube is ignited by a pair of spaced electrodes 20 situatedadjacent thereto andv connected to the terminals of the high voltagesecondary of an ignition transformer 22 whose primary terminals 90 and92 are connected respectively to burner motor terminals 84 and 86, sothat wheneverthe burner I8 is energized an ignitingspark or are playsbetween electrodes 20.

Electric power for the operation of the system is derived from the mainsconnections l0 and I2 which are connected with the burner I8 and a fanmotor 28 through a control unit 32 by connections to be furtherdescribed.

The control unit 32 is conventionally aunitary article of manufactureseparately assembled and sold-to the person making the installation ofthe complete heating system. This. control unit includes a mainsterminal 10 connected to the mains lead l0 through a normally closedlimit switch 12 adapted to open when some selected parameter of furnaceoperation deviates beyond preset limits. In a hot air furnace, thisparameter may be the stack temperature-while in'a', circulating hotwater furnace it may also be the boiler water temperature. The mainsterminal 10 is connected within the control unit 32- by leads 14 and 15with the movable contact 42 of a burner control relay 34. The burnercontrol relay 34 is provided with an operating winding 36 which, whenenergized, attracts movable con tact 42 bringing it into engagementwithfixed contact 38 connected with the burner control terminal which islinked by lead 82 with burner motor terminal 84. The energizing circuitfor the burner motor I8 is completed by the lead 88 extending betweenburner motor termi-' nal 86 and the mains lead I 2.

'The operating winding 36 of burner control relay 34 has one leadconnected with mains terminal I20 through a connecting line I22 andthence to mains lead l2 via connection I24. The other end of operatingwinding 36 is'connected by lead ll8 with the operating 'bimetal 680i asafety switch 59'. Theoperating bimetal'lill hasthermally associatedtherewith an actuating heater '82, whose connections and operation will"operating bimetal 60 away from compensating bimetal 64 releasing thelatch bar 68 which then snaps to the dashed line position indicated. at60', Because of the bias on latch bar 68, it will remain in thisposition until reset by a force'supplied as indicated.

The operation of the safety switch 59, and

burner control relay 34 is influenced by the singlepole double-throwoverlapping contacts 54, 56 and 58 operatively associated with thewinding 48' of I flame relay 46. The safety switch heater 62 isconnected between thecompensatin'g bimetai (i4 and? thenormallyeng'aged'fixd contact 54. The

movable-v contact 58 of flame relay 46 is linked with the thermostatterminal )2 through the connecting-lead I 05, whilean alternative powercircuitextends from normally disengaged" fixed contact 50 throughnormally open contacts 40 and '44 of burner relay 34 and lead I I6to'the compenlead M8 to" operating winding and thence through lead' I22,mains terminal I20 and lead I24tothepowermainl2f- I The operatingwinding 48 of the flame relay 46 is connected to combustion monitorterminal I34 through lead I36 and with mains terminal I20 through lead38," In addition to the earlierrecited flame relay contacts, there isalso-present anormally open contact pair '50, 52 connected withthe'circulator controller terminals I44'and 45 shown'connect'ed inparallel'with a limiting inductance I28. The faln 28 has one power inputterminal i42 connected with power main I2 and another-power inputterminal- I connected to the power maintflthrough the'limitinginductance H8 and lead I26. When the flame relay 46 i'senergizecl, thecircuit. across the limiting inductance E28 is closed, removing thisimpedance from the circuit to permit full speed operation ofthe fan- IThe operation: of the flame relay 40 is con trolled by temperatureresponsive resistor 24 located within the combustion chamber I6 adjacentthe inner end. of the burner blast tube. This resistor may be asemi-conductor consisting essentially of a, ined mixture of'ball clayand ierric oxide, and characterized by relatively low resistance inthepresence of the high temperatures accompanying combustion whilepresenting substantially an open' circuit at normal ambienttemperatures; The resistor 24; has one terminal connected with the powermain I0 through leadsI26 and H0, while. its other terminal is linked bylead 132 with combustion monital-terminal. I34. j

-The, control unit 32 is provided with a pair of thermostat terminals 04and I02 connected respectively withmainsterminal f0 and movable contactEifof fiame'relay 46. Operation. of the over-all system is under thecontrol of a-thermostat 08 connected to thermostat terminal 84 4 Ithrough a lead 96 and having associated there-' with a contact I00connected with thermostat terminal I02 through the line I04.

Operation It will be noted that there is a permanently connected powersupply ior the fan 20 through the limiting reactor I20. {This reactormay be located externally of the'control'unit as'illustrated in thedrawings or, where the circulator motor requires but low power, may bemounted on the control unit itself. The current normally passing throughthe inductance I28 operates the fan 28 ata predetermined minimum speedwith a resulting constant intake of air at the return inlet 30. Thethermostat 98 is located adjacent the return register 30'and responds tothe temperature of the return air, which is indicative of thetemperature of the space whose condition is being controlled. Upon'reaching a predetermined minimum temperature, contact I00 i's engagedcompleting the following I energizing circuit for burner relay 34: mainslead I10; limit switch I2. mains terminal I0, connection Y 14 thermostatterminal 94, lead 96, thermostat 98, contact I00, line I04, thermostatterminal I02, lead I00, cen'- tral contact 56, back contact 54, heater62, compensating bimetal 6 4, latch bar 68, operating bimetal 60, Iead II8, operating winding 35, lead [22, mains terminal I20 and lead i2-4to-mains lead I2. Thi pulls in the contacts of burner relay 34, closingthe following power circuit to the burner motor'IB: mains lead I0,limitswitch' I2, mains terminal-F0, leads 14, I5, contact 42', con tact38", burner control terminal 80, line 82, burner terminals 84and 86, andline 88 to mains; lead $2, This sets theburner in operation -thedelivered combustible spray bein ignited by {the spark discharge acrosselectrodes 20. Sincethe combustion sensing resistor 24 requires anappreciable time to heat up, however, the flame relay 46 remainsdie-energized for a time. At'the same time that the burner control relay34 closes the energizingcircuit for burnermotor I8, an auxiliary powercircuit for the burner control relayis partially 'set up throughcontacts 40 and 44.; This, circuit extends from-"compensating bimetal 04through lead H6, contacts 40, 44 and lead II2 to'the front contact 58 ofthe-single-pole double-throw switch assembly on flame relay '46. Sincethe contact 58 is at this time disengaged, the auxiliary power circuitdoes not at once influence the operation of the system. When theresistor 24 has attained a sufliciently high temperature, the currentflow-through; flame rclay 46 reaches the'operating' value and actuatesthe associating contacts. This closes contacts. 56 and 58 whiledisengaging contact 54 in an overlapping manner. Thecircuit through theresistor 02 has now been interrupted and an alternative circuit closedextending from thermostat terminal I02 through, lead I06; contacts 55,50. lead II 2, contacts 40, 44 and lead [I6 to: the compensating bimetal64, and thence through the operating winding of burner controlrelay 3.4to maintain this relay energized. At the same time. contacts 50, 52close, short-circuitirig the. limitin inductance I28. to permitoperation, oizthe. fan 20 at full speed.

Operation of the burner motor I8 continues'until the thermostat 9B is.satisfied, at whichtime the thermostat terminal I02 is disconnected atthe thermostat from the power supply to de energize burner control relay34 and interrupt burner operation, simultaneously opening contacts 40and 44. The opening of the thermostat, however, is without effect on thecombustion sensing energizing circuit for the flame relay 46, whichremains in energized condition holding the contacts 50 and 52 closed tomaintain the fan 28 at full operating speed until the furnace hascooled, after which the increase in resistance of combustion sensingresistor 24 diminishes the current through the operating winding 48 offlame relay 46 below its holding value, dropping out contacts 50 and 52to return the fan 29 to slow speed operation.

In the event that combustion is not established, flame relay 46 is notenergized, whereby the operating current for burner control relay 34 continues to flow through the safety switch heater 62, warping theoperating bimetal 60 away from compensating bimetal 64 to release thelatch bar 68 and open the safety switch.

Should combustion fail during a normal operating cycle, the resistor 24will increase in value ultimately causing the drop-out of flame relay 46to restore the flow of operating current for burner control relay 34through safety switch heater 62 which, after a predetermined time, againactuates the safety switch 59 to open circuit position.

Should the heater 62 be burned out, the system cannot be placed inoperation, since the starting circuit extends therethrough. It is thusfail-safe in this respect.

If the furnace temperature becomes too high, limit switch 12 opens,tie-energizing the burner control relay 34 to discontinue burneroperation. However, the fan and combustion sensing circuits areconnected to the power mains independently of limit switch 12, wherebyflame relay 46 remains energized, holding the high-speed fan circuitclosed to assist in cooling the furnace.

Should the thermostat be manually actuated to open circuit and thenagain to closed circuit position during a normal operating cycle, theburner will not be immediately restored to operation because the flamerelay 46 remains energized, holding movable contact 56 in engagement-With front contact 58, and out of engagement with back contact 54.Drop-out of the burner control relay 34 opens the auxiliary contacts 49,44 so that when power is re-applied there is no longer any circuit forthe operating current oi burner control relay 34. It cannot flow throughthe safety switch heater 92 because this circuit is open at contact 54,and it cannot flow through the auxiliary power circuit to compensatingbimetal 64 because this circuit has been opened at contacts 40, 44. Notuntil the combustion chamber has cooled sufliciently to drop out theflame relay 46 will another operating cycle be initiated. Dangerouspuffs are thereby eliminated.

The foregoing has made the essence of the invention clear and there willbe apparent to those skilled in the art many mo diflcations andapplications which do not distinguish substantially therefrom.

What is claimed and desired to be secured by United States LettersPatent is:

1. In combination, heating apparatus including a combustion chamber anda heat transfer medium circulating system having delivery and returnvents, said medium circulating system being in heat exchangerelationship with said combustion chamber, a thermally responsive switchadjacent said return vent, an electrically operable burner, a thermistorthermally associ ated with said combustion chamber, a limit switch, aburner control relay connecting said burner with a power supply, saidburner relay having an energizable coil, a safety switch connecting saidburner relay coil with said power supply through said limit switch andsaid return vent circuit controller, an electric actuator for saidsafety switch receiving energy. through said burner relay coil, anelectric motor driven fan moving said medium between said return anddelivery vents and connected with said power supply through a circuitnormally energizing said motor for relatively low speed operation, aflame relay having an operating winding connected with said power supplyand with said thermistor associated with said combustion chamber, a setof flame relay controlled contacts disabling said safety switch actuatorin the presence of combustion in said chamber, and means completing ahigh speed power circuit to said motor when said safety switch actuatoris disabled.

2. In combination, an electrically operable burner, a combustion chamberhaving a heat transfer medium in heat exchange relationship therewith,an electric fan for circulating said heat transfer medium, a burnercontrol relay having an energizing coil, a pair of electrical conductorsconnected to a source of electric energy, a normally conductive limitswitch becoming nonconductive when a selected condition varies beyond apredetermined range, a normally closed safety switch, an electricallyresponsive actuator for opening said safety switch after apre-determined interval of current flow through said actuator, a flamerelay having an energizing coil, a first normally closed switch and asecond and a third normally open switch, said last-named switches beingcontrolled by said flame relay and opening and closing, respectively,upon energization of said flame relay, a thermistor associated with saidcombustion chamber, said thermistor and said flame relay coil beingconnected in series across said pair of conductors, said thermistorpermitting an energizing current to flow through said flame relay coilin response to flame in said combustion chamber, a first power circuitconnected across said pair of conductors through said limit switch andincluding said burner relay coil, said safety switch, said actuator andsaid first normally closed switch, a second power circuit connectedacross said pair of conductors through said limit switch and includingsaid burner relay coil, said safety switch, and said second normallyopen switch, and a fan energizing circuit connected across said pair ofconductors independently of said limit switch, said last-named circuitincluding a current limiting device shunted by said third normally openswitch.

3. The combination defined in claim 2, wherein a thermally responsiveswitch is included in said first and second power circuits.

PAUL G. FRERER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,648,924 Warrick Nov. 15, 19272,143,569 Nessell Jan. 10, 1939 2,160,592 King May 30, 1939 2,167,227Wilson July 25, 1939 2,230,446 Baker Feb. 4, 1941

